1. Field of the Invention
This invention relates to a large-area radiator with a front pane and a rear element, wherein the front pane is kept apart from the rear element by spacer elements, a gaseous filler is introduced into the space between the front pane and the rear element and is at a lesser pressure than the pressure of the surrounding atmosphere, and the front pane is made of a glass material.
2. Description of Related Art
Transmissive LCDs require background illumination by a strong light of homogeneous luminance, reduced thickness, low rate of breakage during assembly and handling, and with a great strength over time. Gas discharge lamps with a filling of a noble gas at underpressure meet the requirements of homogeneous luminance and low heat emission. These lamps can also be designed as large-area radiators.
The main mechanical components of such large-area radiators are the front and rear pane and spacer elements for keeping the front and rear panes apart. Front and rear panes made of glass are preferred. It is known to provide rear panes made of glass with reflecting coatings, or foils.
Large-area radiators are known, wherein the discharge current flows through “folded” channels between the front and rear panes, which requires an operating voltage of several hundred Volts (Company Publication “Flat Candle Backlight Products for 4″ Diagonal LCD”). Large-area radiators are also known, in which the current flows directly from the rear to the front pane. Such large-area radiators are operated in connection with LCD applications with operating voltages of only approximately 10 V.
A considerable disadvantage of large-area radiators with an underpressure filling is the great thickness and large weight. The thickness is the result of the minimum discharge distance and of the thickness of the glass panes for the front and rear panes. The pane thickness is the result of strength requirements.
Large-area radiators with front and rear panes of approximately 2.5 mm thickness, which are maintained at an essentially even distance of 40 to 50 mm by spacer elements, are known. FIG. 1 shows a section in a perspective view, taken through a known large-area radiator, in which the front and rear pane and parallel, continuous, strip-shaped spacer elements are shown. It is known that when employing thinner glass panes for the front and rear pane, for example for weight-saving or for reducing the thickness of the large-area radiator, the following problems occur: too large mechanical stresses in the panes; too great bending of the panes between spacer elements; and buckling, tipping over or tearing off of the spacer elements.
The mechanical stresses in the panes because of the exterior pressure are considered to be a main problem. The tensile stress at the exterior surfaces of the pane is on a scale of approximately σ×a(w/t)2, wherein t identifies the pane thickness and w the distance between the spacer elements. When the pane thickness is reduced, it is also necessary to reduce the distance between the spacer elements. It is assumed that with a pane thickness t=2.5 mm, a distance between the spacer elements of at least w=40 to 50 mm is required to keep the tensile stress at the exterior surface of the panes below approximately 10 MPa (expected fatigue strength of class). At a pane thickness of 1 mm, a distance between the spacer elements of less than 20 mm would therefore be required. This results in an increased production outlay and a reduction of the light yield because of the many spacer elements. This assumption has prevented the production of large-area radiators with thinner front and rear panes, or with a greater distance between the spacer elements.